One common application for thermal sensors is in thermal (infrared) detection devices such as night vision equipment. One such class of thermal detection devices includes a focal plane array of infrared detector elements or thermal sensors coupled to a substrate with a corresponding plurality of contact pads between the focal plane array and the substrate. The thermal sensors define the respective picture elements or pixels of the resulting thermal image.
One type of thermal sensor includes a pyroelectric element formed from a pyroelectric material that exhibits a state of electrical polarization dependent upon temperature changes in response to thermal radiation. Barium strontium titanate (BST) is one example of such pyroelectric material. In one embodiment, an infrared absorber and common electrode assembly is disposed on one side of the pyroelectric elements. A sensor signal electrode is disposed on the opposite side of each pyroelectric element. The infrared absorber and common electrode assembly extends across the surface of the focal plane array and is coupled to each of the pyroelectric elements. Each pyroelectric element has its own separate sensor signal electrode. Each infrared detector element or thermal sensor is defined, in part, by the infrared absorber and common electrode assembly and a respective sensor signal electrode, which constitute capacitive plates, and a respective pyroelectric element, which constitutes a dielectric disposed between the capacitive plates.
To maximize thermal response and enhance thermal image accuracy, each pyroelectric element of the focal plane array is preferably isolated thermally from the associated substrate and from adjacent pyroelectric elements to ensure that the sensor signal from each thermal sensor accurately represents incident infrared radiation. Several approaches have been used to enhance both pixel-substrate thermal isolation between the thermal sensors and an underlying substrate and inter-pixel thermal isolation between adjacent pyroelectric elements.